The overall objective is to explore the surface chemistry of teeth as it relates to caries resistance. A study of the concentrations of lead in saliva and surface enamal of teeth in situ is under way on a group about 250 school children in Cambridge, Mass. Preliminary findings have shown prolonged elevated levels of strontium in saliva after ingestion of strontium lactate. Also strontium tends to accumulate in salivary sediments, presumably due to protein binding. These studies will be continued. A method for measuring the permeability of enamel, involving back diffusion of iodide, will be refined for use in vivo, and employed to assess changes in enamel permeability under physiological and experimental conditions. Measurable quantities of peptides and free amino acids have been extracted from the enamel of single teeth by water and weak acid buffers. Procedures for peptide mapping and amino acid analyses of the minute samples will be worked out. Histological studies have shown that caries penetrate the enamel along the interprismatic substance, indicating that this structure is relatively caries susceptible. The interprismatic substance has been isolated and shown to be higher in protein, magnesium, sodium and CO2 than the prism cores. These analyses will be extended to trace elements. The fluoride deposited in enamel from single topical treatments (5 min) with various fluoride solutions has been found to consist primarily of calcium fluoride and of only small amounts of apatitic fluoride. Attempts will be made to increase the formation of apatitic fluoride by the use of coatings designed to prolong the contact between the applied fluoride and the enamel surface. BIBLIOGRAPHIC REFERENCES: Brudevold, F., Bakhos, Y., and Srinivasan, B.N. Separation of human enamel structures by density fractionation. Archs oral Biol. 21: 113-119, 1976.